Corrosion inhibitors and method



United States Patent-Q 7 ,r 2,824,782 coRRosIoNmHIorrons ANnMErHoD Frank Ross andCharles Mellick, Chicago, Ill., assignors to 'DearhornChemical Company, Chicago, 11]., a corporation of Illinois No Drawing. Application October 4, 1955 1 Serial No. 538,521 7 14 Claims. (CI. 21-25) should preferably prevent such corrosion as well as 'protect against mechanical damage.

The basic concepts of corrosion and its causes are fairly well understood.-- For example, steel rusts in-the atmosphere because of achemical reaction of the steel with moisture and oxygen in the air. The oxygen in the air is a relatively, constant proportion, although the moisture content in the air varies considerablyxlt is generally understood that the'prese'nce of oxygen and water is required for rusting tooccur. The removal of oxygen from an atmosphere in which a metal article is packaged is an extremely difiicult and impractical operation. Heretofore, protective packaging of metals has usually been based upon the provisions of some sort of means for minimizing direct contact between moisture and the metal. 7 Oilor grease coatings may be applied directly to the metal for this purpose. Waterproof .wraps or packages have also been suggested. Other moistureexcluding methods include the use of strong moisture, absorbing materials placed within a waterproof package containing the metal articles.

Recently, however, there has developed a very great interest in what is known as "vapor-phase inhibitorsfi which are unique in that they prevent corrosion when both moisture and oxygen are present in the atmosphere in which a metal article is packaged. The exclusion of one or both of these essential corrosion inducing agents, viz, moisture and oxygen, is not necessary. Most preferably these vapor-phase corrosion inhibitors are applied to a suitable paper web or the like packaging means and the metal'article is wrapped therein. It is not necessary to maintain the paper in contact with all of the surfaces of the metal article so wrapped, since the vapor-phase corrosion inhibitor apparently volatilizes very slowly so as to release agents into the atmosphere which effectively prevent corrosion of the metal that is adjacentto as well as touching'the vapor-phase corrosion inhibitors. The rate ofvolatilization of a preferred corrosion inhibitor isjextremely slow, fact almost imperceptible. How ever, the reasonthat no rusting occurs is understood to bethat the inhibitor; volatilizes or-releases a volatile material therefrom"which permeates the air surrounding the metal 'article within thef package. The inhibitor does not react with or remove water or oxygen, nor does 'it make anygappreciablechange in:the determinable properties such, as the pI-Iof moisture in the vicinity. Also, theiinhibitorl is notconsumed to any appreciable; extent byiits ac lTh 2 not necessarily to-the properties-which various inhibitors that have been proposed orare actually incommercial usemay possess. Instead, almost all of such inhibitors leave something to be desired; either -in' performance or inaeconomic respects or both. n

The instantinvention is based upon .the discovery of certain new, inexpensive and particularly suitablevaporphase corrosion inhibitor compositions which consistessentially of .an. acid salt having the formula:

I RCOOHiRCOOM I wherein M is an alkali metal and each RC0 is .a long chain fatty acyl group, and one of, said-R's aC -C radical and the other R. is a C5-C17 radical. The acid soaps or saltsarea known class of compounds as.es tablished, for example, by Dr. A. W. Ralston in fFa'tty Acids and Derivatives, page 888, and they are under.- stood to have the formula above shown resulting from 50% neutralizationofa fatty acid, wih a suitable alkali. The fatty acidflfperuse.,are..substantially ineffective as corrosion;inhibitors;r,Certain salts of the fatty acids (i. e., completelyneutralized salts) have shown some corrosion inhibiting, properties, but the instant acid salts possess, a uniquepombination ofproperties most advantageousforfthe sd alled vapor-phase corrosion inhibi: tion., f J4 1 v r In Un' ed State's PatentNo. 2,126,173, issued to Clapsadle on August 9, l938, there is described an aqueous alcoholic composition,- such as'an anti-freeze composition, which contains sodium nitrite and certain ;higher fatty acids, such as oleic, palmittic and stearic acidi'and/or triethanolamine salts thereof. The nitrite and them-i: ethanolamine salts are presumably added for thepurpose of preventing corrosion in the liquid phase, and there is no teaching in Clapsadle concerning the use of these ingredients in vapor-phase corrosion inhibition. Moreover, the applicantshave tested sodium salts of these higher fattyacids (with or without sodium nitrite) and found them to be definitely inferior to the compositions of the instant invention as vapor-phasecorrosion inhibitors., H l

In United States Patent No. 2,173,689, issuedio Lamprey on September 19, 1939, another aqueous alcohol composition is suggested containing, as liquid phase corrosion inhibitors,-sodium nitrite plus a. sodium salt of certain unsaturated organic acids. The specific acids suggested are crotonic, maleic, cinnarnic andfuryl acrylic acids, Again, there is no suggestion concerning the use of such corrosion inhibitors in vapor-phase cor,- rosion, .rather than the liquid'phase corrosion described by Lamprey. Moreover, it has been found that-aryl and heterocyclic carboxylic acid salts (such as the cinnamioand fury] acrylic acid salts suggested by' Lam.- prey) are not operative as vapor-phase corro'sionginhibitors,:whenused alone or in conjunction with sodium nitrite A recently, published Government publication (manuscript submitted January 29, 1954, and published March 10, 1954) entitled Volatile Rust Inhibitors by Hayward R. Baker of the Naval Research Laboratory, Washin'gton, D.: C.,.designated as NRL Report No. 14319 sum: marizes-some aspects of the overall problem'zhere in volved and also summarizes the findings of-. .the' Naval Research Laboratory. This report shows, among other things, that so-called inhibitors useful in aqueousalcohol' solutions are often noteffective as vapor-phase corrosion inhibitors, and from this it could be concluded that a suggestion that an inhibitor may be used in aqueous alcohol media does not amount to a suggestion that this-inhibitor is a yaponphase inhibitor. It will benon.page:.l5 of the Hayward report conclusion alk metalsalts oforganieacids do not possess sufiicient vapor'pressureto 'be-eflic ient rust" inhibitors. The instantinvention, however, is based 1 uponthe discovery of the unique effectiveness of certain acid salts as vap or-pha'se'corros'ion inhibitors.

Itis; therefore; an important object of the instant -invention to provide .a :new and improved vapor-phase corrosion inhibitor as well ;as; an improved vapdr pha'se 7 corrosion inhibiting procedure andpackaging material. 7 7' corrosion inhibitor, consisting essentially of a certain specific acidsaltg.

" A furtherfobject'of the 'insta'ntfinventionjis 'tio'pfovi def anf' imprloved "method of pfotecting jmetal from atmfospheric c'o'rro's'i'on, that comprises positioning in "the gi'mmediate "vicinity .of the mjetal an 'efiective/quaritit' of 7 a'ce'rtan specific acid salt to'b'e desc'rib'ed'indetailiherein- Othe r;and further objects, "features i and" advantages of the'present'invention will becomeapparent to'those-skilled ln the art from the followingdetailed disclosure thereof and examples of preferred embodiments thereof. I

The invention consists in a carrier-or wrapping paper containing 'a vapor-phase corrosion inhibiting..coniposi tron 'and'a'process using iSllCh composition for the "protection of metal, which composition consists essentially of'ana'cid salt havingthe formulaj i] 7 "genome/00M,- V wherein 'is-yan alkali metal and each RCO-is 'a long chain fatty {acyl group; andfon'e' of said Rs is -'a 6 C2 radicaland the other of said R3 is a C -C ;-radical.

Althbiig'hiit isfnot desired to limit 'theiinstant inven tion many particular theory; it is believedthat-ertain I aspects 1 of the "instant'invention can be 'ei plained by cer with, it'niust be assumed that an effective vapor-phase W inhibitor 'yolatilizes and/ or rgives -ofi a -volatilelr'naterial inorder toobtain the resulting inhibiting effect; The volatile material is-furtlier believed to forrn' an extremely thin '(monomolecular) impervious film on the metaLsurface. The particular character of this impervious 'film.

is-not clearly u'ridefstoodexcept that it tends mprevemcorro'sivleaction. Thepa'i'ticula'r mechanics of the chemithesereactions must also --ihvolv'e-the formation of an 1.12am: .least voiieftsf are j r n t gw t a J.

I of=distilled water anda;

not the "RC0 "groups must "be a "GFGm fatty-acyI group} V 7 (preferably a .Cg-Cn fatty acyl'group).

stantacid salts 'may b e formed of 'mix ed ac "ample being sodium ac pr 'formed by' 50%neutrf1i'zat1on with sod um'hydroiideof an'equimolar mixture of caprylic'andstearic acids. 'The acid sal sirnayzalso, .Q 1r;s;e :he altsaqfte; single acid Expressed ing other terms, each of the Rs is" preferably a straight chain hydrocarbon. radical having from 5 to 17 carbon atoms therein, and one of the Rfs must contain 5 to ,11 carbon 7 atoms therein (althohgh-theothr R may contain as many Y as in the case of sodium .aidmagfrte or sodium acid 'caprylate, each formed by 50%: .neutraliiation with sops used'must 'b .(t g'ronpjaildl'thebllie canb, 2m; 1 9st preferablybothIRsafQCV-Cib" alkyl'gi'oups'. Thebest resnlts havelbn iohtained fusing a e/til. c ptain???" undecylenyl .aeyl group's: t

- dium hydroxideof caprico'r caprylic acids; respectively. p The acids whichmay be used in;the practice-of the instant invention include the following: 1 'i -(C Hexanoic.(caproic),- hexenoic,ietc;:.,j .2. (C Heptanoic (oenanthicl,jhepte, to; i

.(C ').-.Octanoic ;(caprylic)eoctenoic, (C )*Nonanoiclpelargonic);nonenoiefifi -r i m) Decanoic:(cap1i.),de mbi gietc-g .1 :1. ,(.C )..'Hendedecanoic,'hendecenoicinndecylenicy etg; 7 '25 (C .Dodecanoiclltlauriclc,itch.

(C Tetrade canoic (myris, r 411:. (Cm).Hexadecanoicipalmif )1: i 1 u 1 :(c Octadecanoic. istear zh'iocta er enqic .(Q 7 19 5 1 Examplesgof the yprq aratibnaf the 'inst i i d 'sal si I 1 taiii ehemicalr'r'eactions and/or 'pheno'menar To begin 1 z -fi sew-21 9 sebt i nq t. na eslcentsel s' m i The addition of 20 Ulla Of methanglprfiodnces a lear t: T

solutionoftheacid salt.

' aha-ada ant; ami e Y A clear solution is also produced'by'dissolving:28.8 I

sodium 'hydroxide{in-'a1mixtureof '45 f of -methanol etfectivewvolatile" material The jacids' per -se in-rriost cases eXhibit little or no inhibiting {'eiie'ct and appear i to low vapor pressures such as -to indicate that an irisufii V cient. amount of volatile mate'rial can beprovided there by. The instant acid salts are recog'nized compounds and it is understood that theydifier from' mere'=mixtures V of aflfully neutralized salt and the acid. There is some apparent linkage "between the alkali and i all 1of th'e acid present inthe instant acid saltsso that these compounds areidefinite chemicalentities, difierin'g fromnormaksoaps' in melting point, solubility, and other'prQperties; -The corrosion :inhibitingeifect resulting from -the us'e .ofthe instant acid salts is much Lgre'aterthan that obtained-using either the'acid or the fully neutralized salt. 1

1 Throughout the instant specification Jthe ateriniaci'd ncoonncooiu wherein M is 7 an alkali ;metal =(tliefpre'dorhinaiit them bers of this group beingfsodiumgpotassium and-lithium and each RCQis-an-acylgronp derived fromfa'lon'g chain fatty acid which mayibeafig fi ffatty acimaltliou'ghone" 1 theLsoIu tion"is cooled toree l temperature j pletely neutralizedrs'alts'fof thefattyacids 'exhibit wry warm 1( SQIll-tionbf 3' 10-05 vmol) acidin 30 m1. methano Ajpre'cipitate for'rnsiwhen i the solution cools below "40" ."The ;a .d;sal t isiformed byadd n z 9 9 L is; (0.11 .m lnf sodium hyd x d in i ttl 0 of water. .pl s-lq; o im hano so ut n 10f .Zl -A -s. s 10.1 ml). Q :saprylic n .nr a q ;i cd even at the boiling' point;-and asol mas S'iz lti'E Sodiuni izciii ei'zpi'ylate ole a'te" A cleajr...solutionlislprodiiced i V V 7 Salt G. Potassium acid caprate A solution of'the acid salt is prepared by dissolving 0.1 mol of capric acid and 0.05 mpl of potassium hydroxide in a hot (60 C.) mixture of 30 ml. of isopropyl alcohol and 20 ml. of distilled waten Salt H -L'ith ium acid caprate A clear solution 'of the acid salt is prepared by dissolving O.1 mol of capric acid and 0.05 mol 'of lithium hydroxide in a'hot (60f C.). mixture of.30 ml. of isopropyl alcohol and 20 ml; of distilled "water.

Salt I.Sdium acid unalecylenatej A solution of the acid salt is prepared by dissolving 0.2 mol of undecylenic acid and 0.1 mol of sodium hydroxide in a hot (60 C.) mixture of 60 ml. of isopropyl alcohol and 40 ml. of distilled water.

Salt J.-Sodium acid caprate'caprylate A clear solution of the instant acid salt is prepared by dissolving 15.8 g. (approximately 0.1 mol) of a com- Salt K.S0dium acid caproate A solution is prepared by dissolving 0.1 mol of caproic 'acid and 0.05 mol of sodium hydroxide in 30 ml. of 'isQ- propyl alcohol and 20 ml. of H 0. 1

Salt L.Sodium acid pelargonate A solution is prepared by dissolving 0.1 mol of pel argonic acid and 0.05 mol of sodium hydroxide in 30 ml. of isopropyl alcohol and 20 ml. of H 0. A

Static performance tests were run for each of the acid salts; In the static performance tests, strips of 30 lbs. neutral kraft paper measuring 4 inches by 5 inches were impregnated with solutions of the acid salts. The strip's were used to line 8 ounce glass jars measuring approximately 15 centimeters in height and 6 centimeters in diameter, and a bakelite cup containing 5 ml. of distilled water was placed in each jar. A rubber stopper with a stainless steel hook therein for holding the steel specimen was employed to close the jar. The steel panels or specimen tests panels, measuring A5 inch by 1 inch by 3 inches, were cleaned by sand-blasting and washed with hot benzene, weighed and suspended in the jars so as not to contact the paper. For comparison, blanks were run with untreated 30 lb. neutral kraft paper. Three series of tests were carried out using the following temperature cycles:

(1) 72 hours at 140 F.,

2 hours at room temperature, 96 hours at 140 F. (2) 48 hours at 140 F.,

2 hours at room temperature, 120 hours at 140 F. (3) 72 hours at 140 F.,

5 hours at room temperature, 91 hours at 140 F.

After the corrosion cycle, the steel panels were removed from the jars in the oven, cooled and weighed without cleaning. The results obtained in the test are shown in Table below:

' ,TABLE 1 Salt (acid) Results resting on the impregnated paper.

Fair: Adherent greasy film; some rust.

Excellent: N o corrosion.

Good: Oily coating; but no apparent corrosion.

Excellent: No corrosiona D0. Good: Greasy coating; but no apparent corrosion. Excellent: No corrosion. Fair: Some rust; but far less than blank.

Poor: Substantial amount of rust.

1 Concentrations or 1oads:used are 1 to 10 g. per sq. ft.

of paper.

.From the foregoing it is apparent that improved results are obtained using C5-C12 acid salts, but the best results are obtained using C -C acid salts.

As will be appreciated, for economic purposes it is most advantageous to use as little as possible of the instantacid salts In the case of impregnation of paper or similarpor ous fibrous web materials which may act as an inert solid. carrier which provides for maximum exposure of the impregnant to the atmosphere, it has been foundthat a minimum amount of approximately 0.05 gram per square foot (and preferably about 0.3 gram per square foot) should be used in order to obtain adequate effectiveness. The amount of the acid salt used may be as high as about 20 grams per square foot, although it is notordinarily necessary to use so great an amount of these acid salts. Most preferably, the amount of acid salt used is 1 to 10 grams per square foot of paper web, and the best results are usually obtained using a total of about .2 to 8 grams per square foot of'the instant acid salts. 1

Another type of corrosion test known as the Dynamic Performance Test (MlLP-3'420) is a standard vaporphase corrosion inhibitor test. Using this test the temperature cycle for Government specifications is two hours at 75 F., 24 hours at 40 F.,' 24 hours at F. and 48 hours at F. In these tests the'specimen is a steel rod polished at both ends which is positioned axially in a glass tube with one of its ends exposed'and the other Moist air is directed into the tube through a bubbler. The instant acid salts pass the dynamic performance test (i. e. preventing any corrosion), and particularly, it has been found that the caprylate salts (salts A and B)"and the caprate salts (salts F and G) give unusually satisfactory results in this test, which also involves a proof that the instant salts are capable of giving off a minimum amount of volatile (corrosion inhibiting) material during the test. The mixed salts D and E also pass this test and give good to excellent results in the static test.

As will be appreciated, the instant invention does not apply merely to wrapping papers but also adapts itself to such uses as stufling materials for closed bearings, etc. Thus an inert porous solid carrier such as cotton flocking might be impregnated with the instant inhibitors and used as padding in a sealed package, or used as a bearing stufling. The amount of inhibitor used is, of course, an efiective amount to carry out the function; and the preferred amounts have been given for 30-lb. kraft. Such amounts can be translated to Weight proportions, but they are here given in g./sq. ft. because the concept of exposing the inhibitor to the atmosphere is thus emphasized. The porous fibrous web preferably employed thus has (for all practical purposes) no thickness, only area. It is also preferably a water-insoluble substantially non-hygroscopic body; in fact, water-resistant or waterimpermeable wrapping materials are most preferred (for example, paper with a wax outside coating).

As will be appreciated, the instant invention contemplates the use of mixtures of the instant acid salts, such nhib or sa d pcsi tupo 1th a g. per square footrof a.vapor-phase corrosion-inhibitor2 7' consisting essentially. of :an acid saltghavingithe? formula:

age

' and sodium 'acid'caprylatercaprqate (which is salt 1).

sequently sprayed orflowedinto cavities,etcrofmachinery or engines :or metallicgparts whereof isoihat-wthe -volatile X i ntegior metallic 'su o inhibit corrosion thereof." 1 a V 'It will be understood that modificationsaudfyar tio'ns flmay' be cfiected without departing tr m-thesp it and V scope o the n vel c ncepts 19 We claim-as our invention:

' 51. A packaging-material for rusting-and 7 corrosion ofimetallic' artieles packaged thereim compris- 15 ing an'inert porous solid carrier containing anseffective quantity of l a v a-por phase' corrosion inhibitor consisting essentially-ofianfacid salt-having theformula: i

rosion zof metallic 1 articles 5 packaged ;-therein,; comprising f 7 an inert porous solid carrier; containing:- an eifective ;=quan- -tity;of a vapor..-phase;c0rrosion.inhibitor consisting essentiallyTofsodium acidrcaprat'eh; a o .7 V 7 3. Apackaging,materialifortinhibitin-g;rusting1and.-cor- ;tity of a vaporrphasecorrosioninhibitorconsistingessentially;of -sodium acid caprylate z is s c V 4. A vpackaging lrnaterial lfor -;inhibiting :rnsting' and corrosion of ';metallicarticles pack-aged therein,' com 35 prising a'ninert porous solid carrier'containing an effective 1 V quantity of a YB-PO I-PHaSLG-IQII QSiOIL.illi'libifiOIrCOIlSiSting t essentially'ofsodium acid:caplfylaterstearate A packaging niaterialior inhibiting rustlnga-ndcorrosion :of metallic articles packaged ith'er'ein, comprising 40 an inert porous solid carrier containing an efiectivequantityi of :a lvapo'rrphase corrosion inhibitor consistinges- ,sentially of :sodium acidgcaprylatesoleatep v .7 V

. .6. Asheetofcwrappingipapervimpregnatedjvith;1Lto10 V V LRCOQHRQDOM 7 wherein lV Lis (an alkali -me tal and :each RC0 is along radical and the other of saidv is a-C -:C';-; radical.

3 qqrrs' sida nhib a ca rrl t -sc sat i v icinityof the metal an efie 51.4 sheet sf g in 355a impregnated with 1 to 10 a s 6a i'apof-phasefcorrosipn"'nhih' acidcapra'te;

phase corrosion inhihitor ,consisting essentially pr an M is woman nin i! the "immediate" phase corrosion inhibitor consisting"essentiallyof' sodium acidcaprateia t I V V V j" 7 11. A method 'of protecting metal ffrorriatmospheric corrosion, thaflcomprises lpo sitioning rin ithe' immediatefi V vicinitymf thermetal an'tetfective Jguantity of-a 'vaporphasei-corrosion inhibitorrconsisting essentially ofz'sodium j acid caprylate.

'12, A me h p pr t qtigg jn ta cm-at ph corrosion; that comprises positioning in the immediate a r a i s -yiinit (ofi the etalnefiective uantitI? .rosion'ofimetallic'articlesgpaclgagedtherein, comprising 0 an inert porous-solidcarrierzcontaining anefiectivequam fi ts mn se corrosion inhibitor consisting essentially 9 an equimolar mixture of sodiurn'acid aprate and sodiurn-acid capryl'ate, ilftnA sthqdr rgtsct i vbr cs on 1: 1am pri e vicinity of the'metalan tiectiv Qu ntity 1 t A corrosion inhibitor consistingessentially of a l i e we sof p y and :sanri zasid gfl fi eutralize h; d ii 7 r i me'm ttg gei emite fiasirhs lsa gaf 7 

1. A PACKAGING MATERIAL FOR INHIBITING RUSTING AND CORROSION OF METALLIC ARTICLES PACKAGED THEREIN, COMPRISING AN INERT POROUS SOLID CARRIER CONTAINING AN EFFECTIVE QUANTITY OF A VAPOR-PHASE CORROSION INHIBITOR CONSISTING ESSENTIALLY OF AN ACID SALT HAVING THE FORMULA: 